This application claims the priority of German Patent Application Serial No. 198 53 582.1, filed Nov. 20, 1998, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a method and apparatus for producing injection-molded parts.
European Patent Specification EP 0 658 410 A2 describes a process in which melt is applied onto the mold surface via a hot runner system integrated in a mold half. The other mold half is disposed hereby at a distance to the first mold half and moved toward the first mold half to the closing position, when melt has been substantially applied onto the mold surface of the first mold half. The melt is spread into all regions of the mold cavity by way of a compression process. This manufacturing process, called swell flow process, is suitable in particular for precise production of large-area injection-molded parts; it has, however, the drawback that at those areas where the melt from the hot runner system reaches the mold surface of the one mold half images of melt exit openings are created in the form of so-called gate marks during the subsequent compression process. These gate marks are unacceptable, especially when optic articles, such as e.g. plastic panes for motor vehicles, are involved.
It is also known, e.g. from the EP 0 597 219, to distribute melt also via the slot die of a nozzle head guided across the mold surface of a mold half. In this process, the lamination is, however, relatively time-consuming and requires a complicated guide system for the nozzle head, for example a robot.
It would therefore be desirable and advantageous to provide an improved method and apparatus, obviating prior art shortcomings.
According to one aspect of the present invention, in a method of producing injection-molded parts in an injection molding machine with an injection mold having two mold halves, melt is applied onto a mold surface of one of the mold halves by a melt feeding device, when the injection mold is open, and the melt is subsequently pressed into all areas of a mold cavity by closing the mold halves, wherein the melt is applied onto the mold surface by a hot runner plate positioned above the mold surface of the one mold half, with the hot runner plate having a plurality of melt feeding nozzles in the form of individually controllable needle seal nozzles.
According to one aspect of the present invention, an apparatus for producing injection-molded parts, includes an injection mold having two mold halves, and a melt feeding device for supply of melt across a mold surface of one of the mold halves, wherein the melt feeding device includes a hot runner plate having a plurality of melt feeding nozzles, wherein the melt feeding nozzles are configured as individually controllable needle seal nozzles.
A feature of the invention is the provision of a separate component, the hot runner plate, to assume the function of the hot runner system, integrated heretofore in a mold half, for spreading the melt substantially evenly onto the mold surface in accordance with the swell flow process via one or more exit ports. The hot runner plate is moved into the open mold only for laminating melt onto the mold surface of a preferably horizontal mold half. Prior to the subsequent compression process, the hot runner plate is moved out. By subdividing this operation, melt can be applied across the mold surface of the mold half free from gate marks.
The functional split has also the advantage that each functional part, that is the mold, on the one hand, and the hot runner plate, on the other hand, can be kept at a temperature optimal for meeting its function.
The hot runner plate may be equipped in any suitable manner with the required needle seal nozzles. Advantageously, a universal hot runner plate can hereby be used which is equipped with needle seal nozzles for applying melt onto the mold surfaces of different mold halves, whereby only the operating profile for the needle seal nozzles needs to be modified. The use of several different molds and a universally useable hot runner plate is thus cost saving.
According to another feature of the present invention, the hot runner plate may be coupled to the other mold half. By way of a shuttle operation, application of melt upon the mold surface of the one mold half by means of the hot runner plate can hereby take place at a same time the finished injection-molded part is removed, outside the closing zone of the mold halves, from the other mold half which is coupled with the hot runner plate. Subsequently, parts to be encapsulated by injection, such as e.g. a frame part of a vehicle pane, can be placed into the moving mold half.
According to another feature of the present invention, the hot runner plate may be coupled with two moving mold halves. In each working phase, i.e. during application of melt onto the stationary or fixed mold half as well as during closing of two mold halves, one mold half is hereby always positioned outside the closing area of the injection molding machine and is freely accessible for handling devices of most different type. There is, for example, the option to withdraw finished injection-molded parts, to place parts to be encapsulated by injection (e.g. frame of a vehicle pane), or to introduce a web material. Basically, this offers also the option to produce with the first moving mold half and the stationary melt-laden mold half a first flat injection-molded part, whereby subsequently melt is again applied from the hot runner plate and then compressed with the second moving mold half. In order to identify only one of the many variations, the second moving mold part and the second melt layer can be pressed jointly with most different insert materials, such as frames, handles, hinges or the like.